Variable displacement engine (VDE) designs can provide increased fuel efficiency by deactivating cylinders during operation modes requiring decreased engine output. Such designs may also incorporate cam profile switching (CPS) to enable high, or low lift valve train modes which correspond to increased fuel efficiency during high and low engine speeds, respectively.
In CPS systems, a VDE design may be supported through a no-lift cam profile that deactivates cylinders based on engine output needs. As an example, U.S. Pat. No. 6,832,583 describes an engine valve train having multiple valve lift modes including cylinder deactivation. The described example utilizes high and low lift cams on the valve train which can be further modified so that low lift corresponds to a no-lift deactivation setting.
However, the inventors herein have recognized that CPS systems such those described in U.S. Pat. No. 6,832,583 may have a limited operating range during higher engine speeds, as they may be unable to robustly switch a cylinder deactivation device such as a solenoid within one engine cycle at higher engine speeds. Further, modifying a CPS system to include a cylinder deactivation device with faster switching capabilities may increase costs and decrease fuel efficiency, as cylinder deactivation devices with faster switching tend to be larger, more expensive, and less efficient.
In one example the above issue may be at least partly addressed by a method for an engine, comprising: adjusting an electromechanical actuator to actuate a cylinder valve adjustment mechanism (such as a VDE mechanism and/or a cam profile switching mechanism), including operating the actuator at a first level without a valve transition, operating the actuator at a second level without a valve transition in response to an increased potential for a valve transition, and operating the actuator at a third level inducing a valve transition, the second level between the first and third levels. In this way, by operating the actuator at selected levels during selected conditions, faster switching may be achieved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.